In engine manufacturing, metal chips and other debris may remain in the engine even when engine parts are cleaned prior to assembly. By their nature, fittings with tapered thread connections create metal chips when assembled into a threaded hole. Machining also may leave metal chips. Casting processes may leave other debris in core passages and crevices. As a result, engines inevitably have some debris inside deep-drilled holes, cast-in core passages, and other places. During engine operation, the heating and cooling of the engine releases this debris into the hydraulic fluid. As the hydraulic fluid flows, the metal chips and other debris move throughout the hydraulic system.
The metal chips and other debris may interfere with proper operation of the engine. This interference is more problematic for engines with hydraulically actuated fuel injection systems. In these engines, a priming reservoir typically is disposed at a level higher than the inlet to the high-pressure pump. The priming reservoir includes a lower reservoir portion usually cast into the engine front cover. An upper reservoir portion is attached to the lower reservoir portion to increase the reservoir volume. A gasket seals the lower and upper reservoir portions. The priming reservoir provides gravity feed to the pump during engine start-up. Any debris in the hydraulic fluid tends to accumulate in the priming reservoir. On engine start-up, the pump drives accumulated debris throughout the hydraulic system. While the engine is running the pump continues to drive debris through the hydraulic system.
Debris in the hydraulic fluid may obstruct sensors, valves, and other parts of the hydraulic system and, especially, the hydraulic-actuating portion of the fuel injector system. Metal chips may clog injector pressure regulators, high-pressure pumps, injectors, and pressure control valves because these parts typically are manufactured to very close tolerances. Even though some parts (e.g., the pressure control valve) have internal filters (e.g., an edge filter), too much debris may clog and prevent proper function of these filters.
Accordingly, there is a need for a filter screen to remove debris from the hydraulic fluid of an internal combustion engine, especially those with hydraulically actuated fuel injection.